Light protection device with a movable opaque shield



\ B. c. NORDMANN 3,548,197

LIGHT PROTECTION DEVICE WITH A MOVABLE OPAQUE SHIELD van 10,19!

Filed March 14, 1969 3,548,197 LIGHT PROTECTION DEVICE WITH A MOVABLEOPAQUE SHIELD Bernard C. Nordmann, Kirkwood, Mo., assignor toMegatronics, Inc., St. Louis, Mo., a corporation of issouri Filed Mar.14, 1969, Ser. No. 807,386 llnt. Cl. G01j 1/42; Gtlld 5/56; (202i 1/30U.S. Cl. 250,-229 21 Claims ABSTRACT OF THE DISCLOSURE This inventionrelates to improvements in light-sensitive, optical, control systems.More particularly, this invention relates to improvements inlight-sensitive, optical, control systems which control electromagneticelements such as solenoids.

It is, therefore, an object of the present invention to provide animproved light-sensitive, optical, control system which controls anelectromagnetic element such as a solenoid.

.As pointed out in George I. Fischer Pat. No. 3,377,427 forLight-Sensitive Optical Control System Fora Television Camera, which wasgranted April 9, 1968, it is important to protect the vidicon or otherlight sensitive tube of a television camera from injury due to-excessiveamounts of light. That patent provides a light-sensitive element whichacts, whenever the light directedi toward the vidicon or otherlight-sensitive tube of a ""le'vision camera exceeds a predeterminedlevel, to cau rotary solenoid to interpose a light-intercepting eleni''iit between that vidicon and the source of light. Thefcontrol systemof that patent requires line voltage which is essentially constant; but,unfortunately, essentially donstant line voltage is not available at alllocations. Consequently, it would be desirable to provide alight-sensitive, opftical, control system for an electromagnetic device,suclii as a solenoid, which could provide prompt and effective actuationof that electromagnetic device despite appreciable variations in linevoltage. The present invention provides such a light-sensitive, optical,control system; and it is, therefore, an object of thd'present inventionto provide a light-sensitive, optical, control system which providesprompt and effective actuation of an electromagnetic device, such as asolenoid, despite appreciable variations in line voltage.

The light-sensitive, optical, control system provided by the presentinvention assures prompt and elfective actuation of the electromagneticdevice controlled thereby, by applying a relatively high voltage pulseto that electromagnetic device to actuate that electromagnetic device.That voltage pulse is so high that it will be able toassure prompt andeffective actuation of that electromagnetic device, even if a sharp dropin line voltage shar'ply reduces the value of that voltage pulse.However, that voltage pulse is so high that it would cause excessiveheating of that electromagnetic device, if that voltage pulse was oflong duration. The light-sensitive, optical, control system provided bythe present invention assures prompt and effective actuation of theelectromagnetic device controlled thereby, by applying a relatively highvoltage pulse to that electromagnetic device to actuate that 3,54%,BWPatented Dec. l5, l i'lll electromagnetic device; and it avoidsexcessive heating of that electromagnetic device during the ensuingenergization of that electromagnetic device by making the duration ofthat voltage pulse short and by using a sub stantially lower voltage tokeep that electromagnetic de-= vice energized. The substantially lowervoltage not only minimizes the heating of the electromagnetic device,but it also reduces the amount of power that is consumed by thatelectromagnetic device. It is, therefore, an object of the presentinvention to provide a light-sensitive, optical, control system whichuses a relatively high voltage pulse to actuate an electromagneticdevice and which uses a substantially lower voltage to keep thatelectromagnetic device energized.

The light-sensitive, optical, control system provided by the presentinvention has a ramp-generating subcircuit which enables that controlsystem to develop the relatively high voltage pulse which is needed toassure prompt and effective actuation of the electromagnetic elementcontrolled by that control system; and that control systern develops aregulated voltage and applies that regulated voltage to the input ofthat ramp-generating subcircuit. The application of that regulatedvoltage to the input of that ramp-generating subcircuit enables thatcontrol system to develop the relatively high voltage pulse which isneeded to promptly and effectively actuate the electromagneticelementeven if the line voltage drops sharply. It is, therefore, anobject of the present invention to provide a control system with aramp-generating su=bcircuit which enables that'lcontrol system todevelop a relatively high voltage pulse, and to develop a regulatedvoltage and to apply that regulated voltage to the input of thatramp-generating subcircuit.

The light-sensitive, optical, control system provided by the presentinvention uses direct current to energize the electromagnetic elementcontrolled thereby, but it senses the amount of light received by thelight-sensitive element thereof during every half-cycle of thealternating current supplied to that control system. As a result, thatcontrol system provides the quiet operation of that electromagneticelement which direct current makes possible, and yet that control systemprovides instantaneous sensing of the amount of light falling upon thelight-sensitive element thereof. It is, therefore, an object of thepresent invention to provide a light-sensitive, optical, control systemwhich utilizes direct current to actuate the electromagnetic elementcontrolled thereby, but which senses the amount of light falling uponthe light sensitive element thereof during each half-cycle of thealternating current supplied to that control system.

Other and further objects and advantages of the present invention shouldbecome apparent from an examination. of the drawing and accompanyingdescription.

In the l-drawing and accompanying description a me ferred embodiment ofthe present invention is shown and described but it is to be understoodthat the drawing and accompanying description are for the purpose ofillustration only and do not limit the invention and that the inventionwill be defined by the appended claims.

The drawing is a schematic diagram of one preferred embodiment oflight-sensitive, optical, control system that is made in accordance withthe principles and teachings of the present invention.

COMPONENTS OF CONTROL SYSTEM Referring to the drawing in detail, thenumeral 1% denote'sa-maI plug which' has prongs that can be insertedinto a socket connected to a suitable source of alternating currentlnthe preferredembodiment of light-sensitive, optical, control systemshown by the drawing, the prongs of the plug 10 will be inserted into asocket connected toa source of one hundred and fifteen volts, sixtycycle, alternating current, The numeral 12 denotes a fullwave, bridgerectifier which includes diodes 14, 16, 1S and 2t and one of the inputterminals of that full-wave, bridge rectifier is directly connected toone prong of the plug while the other input terminal of that full-wave,

bridge rectifier is connected to the lower prong of that plug by a fuse22 and a resistor 24. The resistor 24 acts as a current limitingresistor to protect the diodes 14, 16, 18 and from injury due to excessflow of current through them.

A resistor 28 and two Zener diodes 32 and 36 are connected in serieswith each other, and are connected across theoutput terminals of thefull-wave, bridge rectifier 1 2 by junctions 26, and 34 and by a returnconductor 38-. The Zener diode 36 will determine the maximum voltagewhich can be developed at the junction 34; and the Zener diode 32 willcoact with the Zener diode 36 to determine the maximum voltage which canbe developed at the junction 30.

A. junction 40 connects the upper terminal of a resistor 46 to thejunction 30; and that resistor, a potentiometer 48,, and alight-sensitive element 50 are connected in series with each otherbetween the junction 40 and the return conductor 38. Although differentlight-sensitive elements can be used as the light-sensitive element 50,a cadmium sulphide photocell has been found to be very useful. Thenumeral 32 denotes an NPN transistor; and a junction 42, a resistor 54,a junction 56, and. a resistor Sdconnect the collector of thattransistor to the junction 40. A junction and a resistor 62 connect theemitter of that transistor to the return conductor 38. A resistor 64 anda junction 66 connect the movable contact of the potentiometer 48 to thebase of the transistor 52. A resistor 63 has the lower terminal thereofconnected to the resistor 62 by the junction 60; and it has the upperterminal thereof connectedto the junction 42 by a junction 44.

The numeral 70' denotes a PNP transistor; and the emitter of thattransistor is directly connected to the junction 44, and the collectorof that transistor is connected to the return conductor 38 by a junction72 and a resistor 74. The base of the transistor 70 is directlyconnected to the junction 56; and a resistor 76 is connected between thejunctions 66 and 72.

The numeral 78 denotes a diode which has the anode thereof directlyconnected to the junction 72;; and the cathode of that diode isconnected to the upper terminal of a capacitor 81 by a junction 80. Thelower terminal of that capacitor is directly connected to the returnconductor 38. The numeral 86 denotes a potentiometer which has the upperterminal thereof connected to the junction i it by a junction 82; andthe lower terminal of that potentiometer is connected to the returnconductor 38 by a resistor 88. The numeral 90 denotes a PNP transistor;and a junction '84, a resistor 92, and a junction 98 connect the emitterof that transistor to the junction 82. A capacitor 94 and a resistor 96are connected in series with each other; and the upper terminal of thatcapacitor is directly connected to the junction 84, while the lowerterminal of that resistor is directly connected to the junction 98. Adiode 101) has the anode thereof connected to the movable contact of thepotentiometer 86, and it has the cathode thereof connected to the anodeof a diode 162. The cathode of the diode 102 is connected to the base ofthe transistor 96 by a junction 194-; and a resistor 106 is connectedbetween the junction 104 and the return conductor 33. The diodes 1% and.1112 are provided to compensate for any changes in the temperature ofthe transistor 90.

A junction 1% connects the collector of the transistor 91 to the upperterminal of a capacitor 110; and the lower terminal of that capacitor isconnected to the return conductor 38. A unijunction transistor 112 hasthe emitter thereof connected to the junction 108; and it has thebase-one thereof connected to the return conductor 38 by a junction 116and a resistor 118. The base-two of 4 that unijunction transistor isconnected to the junction 34 by a resistor 114.

The lower terminal of the coil 120 of a rotary solenoid is connected tothe upper terminal of a resistor 126 by a junction 124; and the lowerterminal of that resistor is connected to the anode of a controlledrectifier 1.28. That controlled rectifier preferably is a siliconcontrolled rectifier, and the cathode of that controlled rectifier isdirectly connected to the return conductor 38. A junction 11? connectsthe upper terminal of the coil 120, and the upper terminal of acapacitor .122, to the junction 26; and the lower terminal of thatcapacitor is connected to the lower terminal of that coil by thejunction 124.

The coil 120 of the rotary solenoid controls a lightintercepting element132; and the returning spring, not: shown, of that rotary solenoidbiases that light-intercepting element for movement into the path oflight directed toward the vidicon or other light-sensitive tube, of thetelevision camera with which the control system of the present inventionis used. However, that light-intercept ing element will move out of thepath of that light whenever the coil 120 is energized. The coil 120 andthe lightsensitive element 50 are enclosed within a dashed line 130; andthat dashed line is intended to indicate that the said coil and the saidlight-sensitive elementwill be mounted in one or two enclosures on thehousing of the television camera. 7

The full-wave, bridge rectifier 12 acts as a source of direct current;and the Zener diodes 32 and 36 set upper limits for the DC. voltages atthe junctions Mind 34. The light-sensitive element 50, the potentiometer48, the resistors 46, 54, 5 8, 62, 64, 68, 74 and 76,'and thetransistors 52 and 70 constitute a light level detector 77. Thecapacitors 81 and 94, the potentiometer 86, the re sist-o'rsSS, 92, 96and 106, the transistor 90, 'and the diodes 100 and 102 constitute asubcircuit 109 which acts as a ramp-generator and a current source.-Thecapacitor 110, the unijunction transistor 112, and the resistors 114 and118 constitute a unijunction transistor relaxation oscillator 117.

OPERATION OF CONTROL SYSTEM When the prongs of the plug 10 are insertedinto a suitable socket, current will flow from the upper prong of thatplug via diode 14, junction 26, resistor 28, junction 313, Zener diode32, junction 34, Zener diode 36, return conductor 38, diode 18, resistor24, and fuse 22 to the lower prong of that plug, during thosehalf-bycles of the alternating current when that upper prong is positiverelative to that lower prong. During those half-cycles of thatalternating current when the lower prong of the plug 10 is positiverelative to the upper prong of that plug, current will flow from thatlower prong via fuse 22, resistor 24;, diode 16, junction 26, resistor28, junction 30, Zener'diode 32, junction 34, Zener diode 36, returnconductor 38, and diode 20 to that upper prong. The resulting directcurrent which fiows through resistor 28 and Zener; diodes 32 and 36 isnot filtered; and hence the voltage across the output terminals of thefull-wave, bridge rectifier 12 will start at zero, will rise to amaximum, and will then fall to zero during each half-cycle of thealternating current. Because the Zener diode 36 determines the maximumvoltage which can be developed at the junction 34, the voltage at thejunction will start at zero, will rise to a maximum, and will then fallto 2510 during each half-cycle of the alternating current. Because theZener diode 32 contact with the Zener diode 36.to determine the maximumvoltage which can be developed at the junction 30, the voltage at thatjunction will start at zero, Will rise to a maximum, and will then fallto zero during each half-cycle of the alternating current. In onepreferred embodiment of the control system shown by the drawing, thevoltage at the junction 34 will rise to ten volts and the voltage at thejunction 30 will rise to twenty volts during each half-cycle of thealternating current.

The voltage at the junction 30 will be applied across series-connectedresistor 46, potentiometer 48 and lightsensitive element 50; and thevoltage at the movable contact of that potentiometer will be a functionof the setting of that movable contact and of the effective resistanceof that light-sensitive element.- Since the effective resistance of thatlight-sensitive element will vary with the amount of light impingingupon that light-sensitive element, the voltage at the movable contact ofthe potentiometer 48 will be a function of the light which impinges uponthe light-sensitive element 58. The voltage at the junction 30 also willbe applied across the voltage divider which consists of the resistor-s68 and 62; and that voltage divider will develop a Voltage at thejunction 60, and thus at the emitter of transistor 52-, which will riseto a predetermined value during the first part of each half-cycle of thealternating current, which will remain at that value during the middleportion of that half-cycle, and which will fall to zero at the end ofthat half-cycle. The voltage at the junction 30 also will be appliedacross series-connected resistors 54 and 58, the collector-emittercircuit of transistor 52, and resistor 62; and that voltage also will beapplied across the series-connected emittercollector circuit oftransistor 70 and resistor 74.

The lower portion of the potentiometer 48 and the light-sensitiveelement 50 are connected in series with each other and in parallel withseries-connected resistor 64, the base-emitter circuit of transistor 52,and resistor 62; and, whenever the total resistance of theseries-connected lower portion of potentiometer 48 and the lightsensitive element 58 is appreciably smaller than the total resistance ofseries-connected resistor 64, the base-emitter circuit of transistor 52and resistor 62, insufficient current will flow through thatbase-emitter circuit to make that transistor conductive. Consequently,whenever the value of the light which impinges upon the light-sensitiveelement 50 is great enough to make the resistance of thatlight-sensitive element relatively small, the transistor 52 will becomeessentially non-conductive. As long as the transistor 52 is essentiallynon-conductive, the voltage at the junction 56, and thus at the base oftransistor 70, will be essentially the same as the voltage at theemitter of the latter transistor; and the latter transistor will beessentially non-conductive. At, such time, the voltage at the junction72 will be essentially zero.

Whenever the total resistance of the series-connected lower portion ofpotentiometer 48 and the light-sensitive element 50 exceeds the" totalresistance of series-com nected resistor 64, the base-emitter circuit oftransistor 52, and resistor 62, suificient current will flow throughthat baseemitter circuit to render that transistor conductive.Consequently, whenever the value of the light which impinges upon thelight-sensitive element 58 is small enough to make the resistance ofthat light-sensitive element relatively large, the transistor 52 will beconductive. As the transistor 52 becmes conductive, the resultingvoltage drop across the resistor 54 will make the base of transistor 70less positive than the emitter of that transistor; and hence thetransistor 70 will become conductive. The resulting increase in voltagedrop across the resistor 74 will cause the voltage at the junction 72 tobecome more positive; and the resistor 76 will couple that more-positivevoltage to the base of the transistor 52 via the junction 66, therebyfurther increasing the .conduc tivity of that transistor. That furtherincrease in conductivity will make the voltage at the junction 56, andthus at the base of transistor 70, even less positive than the voltageat the emitter of that transistor, and will thereby make that transistoreven more conductive. Very quickly, the positive feedback provided bythe resistor 76 will cause both of the transistors 52 and '70 tosaturate. Consequently, whenever the amount of light impinging upon thelight-sensitive element 50 is below a predetermined value, thetransistors 52 and 78 will saturate during each half-cycle of thealternating current supplied to the plug 8 lil; and the voltage at thejunction 72 will closely ap proach twenty volts during each of thosehalf-cycles. Ali of this means that aslong as the valueof the lightimpinging upon the light-sensitive element 56 is below a predeterminedlevel, the light level detector 77 will cause the voltage at thejunction 72 to closely approach twenty volts during each half-cycle ofthe alternating current. Further, it means that whenever the value ofthe light irnpinging upon the light-sensitive element 5'8 exceeds thatpredetermined level, the light level detector 77 will cause the voltageat the junction 72 to drop essentially to zero.

Whenever the light level detector 77 causes the voltage at the junction72, and thus at the anode of the diode 78, to exceed the voltage at thecathode of that diode, that diode will he become conductive and willpermit current to flow from junction 72 via that diode, junction 80, andcapacitor 811 to the common conductor 38. That current wilt quicklycharge that capacitor to a value close to the pealc value of the voltageatthe junction 72. The capacitor will tend to discharge throughseries-connected poten tiometer 86 and resistor 88 during those portionsof each half-cycle of the alternating current wherein the voltage at thejunction 72 is less than the voltage at the upper terminal of thatcapacitor; but the values of potentiometer 86 and of resistor 88 will beselected to limit the rate of discharge of that capacitor to a valuewhich will keep the voltage across thatcapacitor' essentially constantas long as the light level detector 77 renders the transistor 78conductive during each half-cycle of the alternating current. As aresult, the capacitor 81 will act as a source of steady DC. voltage forsubcircuit 188.

When the light level detector 77 renders the diode 78 conductive,further current will flow from junction 72 via that diode, junctions'8tl and 82, and the upper portion of potentiometer 86 to the movablecontact of that potentiometer; and then one part of that further currentwill flow through the lower portion of that potentiometer and resistor88 to the return conductor 38 while a second part of that furthercurrent will flow through diodes 168 and 102 and resistor 106 to thatreturn conductor, The resulting voltage drop across the series-connectedupper portion of potentiometer 86 and diodes 100 and 182 will make thebase of transistor 90 less positive than the emitter of that transistor;and hence sufiicient current 'will flow, from junction 72 via diode 78,junctions 88, 82 and 84, parallelconnected resistor 92 and seriescapacitor 94 and resistor 96, junction 98, the emitter-base circuit oftransistor 90, junction 104, and resistor 106 to the return capacitor38, to render that transistor conductive, Consequently, current willflow from junction 72 via diode 78, junctions 80, 82 and 84,parallel-connected resistor 92 and seriesed capacitor 94 and resistor96, junction 98, the emitter-ooh lector circuit of transistor 96, andcapacitor tlllti. The voltage at the junction 72, and thus at the anodeof diode 78, will fall below the' voltage at the upper terminal ofcapacitor 81, and thu tt.,the cathode of that diode, at the end of eachhalf-cycle of the alternating current; and hence that diode will becomenon-conductive. However, the capacitor 81 will act as a power supplywhen the diode 78 is non-conductive; and hence that capacitor will keepthe transistor 90 conductive.

Prior to the time when the light level detector 77 first renders thetransistor 70 conductive, the capacitor 94 will be discharged-thatcapacitor discharging through the path constituted by resistors 92 and96. Because the capacitor 94 is initially discharged, it will constitutea low irnpedance at the instant the light level detector 77 firstrenders the transistor 70 conductive; and, because that capacitor andresistor 96 are seriesed and are connected in paral lel with resistor92, that capacitor will elfectively reduce the resistance in the emittercircuit of transistor .88, Con sequently, the latter transistor willsupply a high value of current to the capacitor 11110 as that transistorbecomes conductive. The high value of' current which the transistor 9t)initially supplies to the capacitor lllltl will quickly charge thatcapacitor; and it will cause the voltage at the junction 108 to exceedthe emitter peak point voltage of the unijunction transistor 112 at anearly point in the halfcycle of the alternating current.

The voltage at the junction 34 is applied across seriesconnectedresistor 114, the base-two base-one circuit of the unijunctiontransistor 112, and resistor 118; and while that unijunction transistorwill be non-conductive during the first part of each half-cycle of thealternating current, that unijunction transistor will be renderedconductive as soon as the charge on the capacitor 110 causes the voltageat the junction 1 08 to exceed the emitter peak point voltage of thatunijunction transistor. When the unijunction transistor 112 becomesconductive, the charge within the capacitor 110 will cause current toflow from the upper terminal of that capacitor via junction 108, theemitter base-one circuit of that unijunction transistor, junction 116,resistor 118, and return conductor 38 to the lower terminal of thatcapacitor; and that flow of current will develop a voltage drop acrossthe resistor 118 which will cause current to flow through thegate-to-cathode circuit of the controlled rectifier 128.

The junctions 26 and 119 and the return conductor 38 placeseries-connected coil 120, resistor 126 and controlled rectifier 128across the output of the full-wave, bridge rectifier 12; and, wheneversufiicient current flows through the gate-to-cathode circuit of thatcontrolled rectifier, that controlled rectifier will become conductiveand energize the coil 120 of the rotary solenoid. The capacitor 122,which is connected in parallel with the coil 120 of the rotary solenoid,will coact with the resistor 126 to filter the sharp current pulse thatis supplied to that coil as the controlled rectifier 128 becomesconductive; and hence the coil 120 will receive a longer-durationcurrent pulse. That coil will respond to that current pulse to urge thearmature of that rotary solenoid, and the light-intercepting element 132connected to that armature, toward retracted position-and thus away fromthe path of the light directed toward the vidicon or otherlight-sensitive tube to be protected by that light-interceping element.

Because the capacitor 94 initially acts as a low impedance, thetransistor 90 will permit the capacitor 110 to charge up to the emitterpeak point voltage of unijunction transistor 112 during the early partof the first half-cycle of the alternating current; and the resultingrelatively long on time of the controlled rectifier 128 will enable thecoil 120 to receive a voltage pulse of about ninety volts. Inasmuch asthat coil is rated at twenty-four volts, the ninety volt pulse is amplylarge enough to enable that coil to apply strong rotative forces to thearmature of the rotary solenoid and to the light-intercepting element132.

At the end of the first half-cycle of the alternating current, thevoltages at the junctions 26, 3t) and 34 will fall to zero; and, as thevoltage at the junction 30 falls to zero, the transistors 52 and 70 ofthe light level detector 77 will again become non-conductive, and thevoltage at the junction 72 will fall to zero. However, the capacitor 81will act as a source of direct current; and it will keep enough currentflowing through the series-connected upper portion of potentiometer 86,diodes 100 and 102, and resistor 106 to keep the base of transistor 90less positive than the emitter of that transistorand thus to keep thattransistor conductive. Also, the capacitor 81 will cause current to flowthrough the emitter-collector circuit of transistor 90 and start ie-charging the capacitor 110.

As the voltage at the junction 34 falls to zero, at the end of the firsthalf-cycle of the alternating current, the voltage at the base-two ofthe unijunction transistor 112 will fall to zero; and hence thatunijunction transistor will be non-conductive. That unijunctiontransistor may become non-conductive even before the end of the firsthalf-cycle of the alternating currentbecause that unijunction transistorwill become non-conductive as soon as the capacitor 110 has dischargedsufliciently to make the voltage at the junction 108 less than twovolts-and, in that event, that unijunction transistor will remainnonconductive until it is rendered conductive during the secondhalf-cycle of the alternating current.

Although the voltage at the junction 26, and hence at the junction 119,will fall to zero at the end of the first half-cycle of the alternatingcurrent, the capacity of the capacitor 122 is large enough so thatcapacitor could, if necessary, cause current to continue to flow throughthe coil 120 of the rotary solenoid for about fifteen milliseconds. As aresult, current will continue to flow through the coil 120, and thusenable that coil to continue to sup-= ply rotative forces to thearmature of the rotary solenoid and to the light-intercepting element132, even after the controlled rectifier 128 becomes non-conductive-asit. will do at the end of the first half-cycle of the alternatingcurrent. This means that at the end of the first halfcycle of thealternating current, the light level detector 77 will permit the voltageat the junction 72 to drop to zero, but the capacitor 81 will keep thetransistor conductive and will be charging the capacitor 110. Theunijunction transistor 112 will be non-conductive, and the controlledrectifier 128 will be non-conductive; but the coil 120 will be applyingrotative forces to the armature of the rotary solenoid and to thelight-intercepting element 132, and that armature and thatlight-intercepting element will tend to continue to move towardretracted position.

During the second half-cycle of the alternating current, the light leveldetector 77 will again develop a voltage, which closely approachestwenty volts, at the junction 72; and a voltage of about ten volts willbe applied across the series-connected resistor 114, the base-twobase-one circuit of unijunction transistor 112, and resistor 118, and avoltage in excess of one hundred volts will be applied across theseries-connected coil 120, resistor 126, and controlled rectifier 128.

The diode 78 Will respond to the voltage at the junction 72 to becomeconductive, thereby applying a further charge to the capacitor 81; andthat diode and that capacitor will supply the current which is needed tocause the voltage across the capacitor to rise to the emitter peak pointvoltage of the unijunction transistor 112. As that unijunctiontransistor becomes conductive again, the capacitor 110 will develop avoltage drop across the resistor 118 which will render the controlledrectifier 128 conductive again; and hence the coil of the rotarysolenoid will have another relatively high voltage pulse applied to it.

Because the capacitor 94 will have retained some of the charge that itreceived during the first half-cycle of the alternating current, theimpedance of series-connected capacitor 94 and resistor 96 will behigher than it was at the beginning of the first half-cycle of thealternating current; and hence the total impedance of parallel-comnected resistor 92 and seriesed resistor 96 and capacitor 94 will behigher than it was at the start of that first half-cycle. However, thatimpedance will still be low enough to permit the capacitor 110 to renderthe transistor 112 conductive during the early part of the secondhalf-cycle of the alternating current; and hence a voltage which isclose to ninety volts will be developed across the coil 120. This isimportant, because the armature of the rotary solenoid and thelight-intercepting element 132 will have appreciable massand henceappreciable inertia; and it is desirable that the voltage applied to thecoil 120 remain at a relatively high level until that armature and thatlight-intercepting element have had sufiicient time to rotate intoretracted position.

At the end of the second half-cycle of the alternating current, thevoltages at the junctions 26, 34 and 72 will again drop to Zero, and theunijunction transistor 112 and the controlled rectifier 128 will benon-conductive again. However, the capacitor 81 will again keep thetransistor 90 conductive. Also, the capacitor 122 will again.

cause current to continue to fiow through the coil 120 after thecontrolled rectifier 128 becomes non-conductive.

During each succeeding half-cycle of the alternating current applied tothe plug 10, the light level detector 77 will cause the diode 78 tosupply a further charge to the capacitor 81; and the subcircuit 109 willcause the tran sistor 90 thereof to supply sufficient current to the capacitor 110 to render the unijur'iction transistor 1112 con ductive.During each succeeding half-cycle of the alternating current, theimpedance of the capacitor 94 will be higher than it was at thebeginning of the immediatelypreceding half cycle-because of theprogressively-higher retained charge in that capacitor-until the chargein that capacitor stabilizes. Thereafter, during succeeding halfcyclesof the alternating current, the additional charge which the capacitor 94receives during any given halfcycle will equal the charge which thatcapacitor loses at the end of that half-cycle as it causes current toflow through the resistors 92 and 96. In the said preferred embodimentof control system shown by the drawing, it takes a total of aboutsixteen half-cycles of the alternating current for the charge in thecapacitor 94 to stabilize; and, during those sixteen half-cycles, thevoltage pulses applied to the coil 120 of the rotary solenoid willdecrease exponentially from about ninety volts to about fifteen volts.The initial voltage pulse, and the immediatelysucceeding voltage pulses,applied to the coil 120 will be so high that they will be able to causethat coil to effect prompt and efiective rotation of the light-intercepting element 132 to retracted position, even if the voltage applied tothe plug drops considerably below its normal value. -As a result, thecontrol system provided by the present invention is able to apply amplystrong rotative forces to the light-intercepting element 132-even inlocations where considerable variations in line voltage are experienced.

As the charge in the capacitor 94 becomes stabilized, the impedance ofthat capacitor will become essentially fixed; and that impedance will beextremely large. At such time, the amount of current which can flowthrough the transistor 90 during a given half-cycle of the alternatingcurrent will be very much less than the amount of chrrent which fiowedthrough that transistor during the first halfcycle of the alternatingcurrent. The resulting longer charging time of the capacitor 110 willcause the unijunction transistor 112, and hence the controlled rectifier.128, to become conductive later during that given half-cycle; and hencethe voltage pulse applied to the coil 120 will be only about fifteenvolts. While the capacitor 94 is being charged and its impedance is low,the subcircuit 109 will act as a ramp-generating subcircuit; but oncethat capacitor has become charged and its impedance is very high, thesubcircuit 109 will act as a current source.

The fifteen volt pulses whichare applied to the coil 126 are amply largeto keep that coil energized; and this is important, because it meansthat the control system provided by the present invention will be ableto keep the light-intercepting element 132 in retracted position, evenif the voltage applied to the plug 10 drops considerably below itsnormal value. As a result, the control system provided by the presentinvention is able to keep the light-intercepting element 132 fromprematurely intercepting the light passing to the vidicon or otherlight-sensitive tube-even in locations where considerable variations inline voltage are experienced.

The voltage pulses of about fifteen volts are amply large to keep thecoil 120 energized; but they will permit that coil to develop far lessheat than it would develop if it was supplied with its rated voltage oftwenty-four volts. Further, the fifteen volt pulses reduce the totalamount of power that is consumed by the coil 120.

As long as the value of the light impinging upon the light-sensitiveelement is below a predetermined level, the transistors 52 and 70 of thelight level detector 77 will be rendered conductive during eachhalf-cycle of the alternating current applied to the plug 10; and thecome quent re-charging of the capacitor 81 will enable the subcircuit109 to render the unijunction transistor 112, and. hence the controlledrectifier 128, conductive during that half-cycle. Consequently, as longas the value of the light; impinging upon the light-sensitive element 50is below that predetermined value, the coil 120 will hold the light--intercepting element 132 in retracted position. However, as soon as thevalue of the light impinging upon the lightsensitive element 50 exceedsthat predetermined value, the impedance of that light-sensitive elementwill decrease sutliciently to make the total impedance of the series-comnected lower section of potentiometer 48 and that lightsensitive elementappreciably less than the impedance of series-connected resistor 64!,the base-emitter circuit of transistor 52, and resistor 62. Thereupon,the current flowing through the base-emitter circuit of that transistorwill decrease to the point where that transistor becomes non-conductive;and, at such time, the voltage at the junction 56, and thus at the baseof the transistor 70, will essentially rise to the value of the voltageat the junctions 42 and 44, and thus at the emitter of transistor 70.Consequently, the transistor 70 will become non-conductive; and hencethe voltage at the junction 72 will drop to essentially zero. This meansthat during the next half-cycle of the alternating current, and duringall succeeding halt cycles wherein the value of the light falling uponthe light sensitive element 50 exceeds the predetermined level, thelight level detector 77 will not develop an appreciable voltage at thejunction 72. As a result, the capacitor 81 will not receive anyadditional charges during any of those half-cycles of the alternatingcurrent.

The capacitor 81 of the subcircuit 109 will have suificient capacity toenable it to keep the transistor conductive for one and possibly two orthree half-cycles of the alternating current after the voltage at thejunction 72 drops to zero, and that capacitor will have sufficientcapacity to raise the voltage at the upper;terminal of the capacitor 110to the emitter peak point voltage of the unijunction transistor 112 onceor possibly twice. However, very quickly, the chargejn the capacitor 81will dis sipate to the point where the voltage at the upper terminal ofthe capacitor 110 will be unable to reach the emitter peak point voltageof the unijunction transistor 112. Con sequently, in less than threehalf-cycles after the value of the light impinging upon thelight-sensitive element tl increases above the predetermined level, the'unijunction transistor 112 will remain non-conductive, and hence thecontrol rectifier 128 will remain non-conductive. While the capacitor122 will be able to keep the coil of the rotary solenoid energized forabout fifteen milliseconds after the controlled rectifier 128 becomesnon-conductive, the restoring spring of that rotary solenoid will thenstart moving the armature of that rotary solenoid and the light-'intercepting element 132 toward the path of the light directed towardthe vidicon or other light-sensitive tube. In the said preferredembodiment of control system shown by the drawing, it takes thereturning spring of the rotary solenoid only about one hundred andtwenty milliseconds to move the armature of that rotary solenoid and thelight-intercepting element 132 into the path of the light directedtoward the vidicon or other light-sensitive tube; and hence that controlsystem permits the light-intercept-= ing element 132 to be moved intolight-intercepting position in less than one-fifth of a second after thevalue of the light impinging upon the light-sensitive element 5%increases above the predetermined level.

The returning spring of the rotary solenoid will hold the armature ofthat solenoid and the light-intercepting element 132 in thelight-intercepting position, as long as the value of the light impingingupon the light-sensitive element 50 is above the predetermined level.However, as soon as the value of that light falls below thatpredetermined level, the impedance of that light-sensitive element willincrease sufliciently to cause the transistor 52 of the tight leveldetector 77 to become conductive again. Thereupon, that light leveldetector will cause the subcircuit 109 to charge the capacitor 110 ofthe unijunction relaxation oscillator 117with a consequent firing ofunijunction transistor 112 and of controlled rectifier 128. Because thecapacitor ?4 became fully discharged through resistors 92 and 96, whilethe value of the light impinging upon the light-sensitive element 50 wasabove the predetermined level, that capacitor will again act as a lowimpedance, and thus will permit a large value of current to flow throughthe transistor 90. The resulting prompt charging of the capacitor 110will cause the unijunction transistor 112 and the controlled rectifier128 to be rendered conductive during the early part of the half-cycle ofthe alternating current. This means that the coil 120 of the rotarysolenoid will again receive a voltage pulse of about ninety volts; andthat voltage pulse will enable that coil to start rotating the armatureof that rotary solenoid and the light-intercepting element 132. towardlight-intercepting position. The coil 120 will receive further highvoltage pulses during succeeding half-cycles of the alternating current,and those high voltage pulses will assure prompt and certain rotation ofthe light-intercepting element 132 into light-intercepting position evenif the voltage applied to the plug drops considerably. After the chargein the capacitor 94 becomes stabilized, the voltage pulses applied tothe coil 120 will be about fifteen volts; all as explained hereinbefore.Consequently, the coil 120 will be able to hold the light-interceptingelement 132 in light-intercepting position without experiencing undueheating.

The relatively high voltage pulses which are applied to the coil 120, asthat coil moves the light-intercepting ele- :ment 132 to retractedposition, are very desirable; because they enable that coil to move thatlight-intercepting element to retracted position even when appreciabledecreases in line voltage are experienced. The sharply lower voltagepulses which are applied to the coil 120, as that coil holds thelight-intercepting element in retracted position, are very desirable;because they avoid undue heating of that coil, and because they reducethe amount of power consumed by that coil. The action .of the Zenerdiode 36 in providing a regulated voltage for the base-two baseonecircuit of the unijunction transistor, and the action of the Zener diode32 and 36 in providing a regulated voltage for the light level detector77, are important: in making the voltage at the base of the transistor52 essentially dependent upon the amount of light impinging upon thelight-sensitive element 50 and essentially independent of changes inline voltage. The action of the Zener diode 36 in providing a regulatedvoltage for the light level detector 77, is important in enabling thecontrol system to apply properly-timed voltage pulses to coil 1% despitechanges in the line voltage.

The positive feedback provided by the resistor 76 causes hoth of thetransistors 52 and 70 to become conductive at the saturation level assoon as the transistor 52 becomes conductive and that positive feedbackcauses both of those transistors to become non-conductive as soon as thetransistor 52 becomes non-conductive. As a result, prompt development ofabout twenty volts at the junction 72 is assured when the plug 10 isinserted into a socket at a time when the amount of light impinging uponthe lightsensitive element 50 is below the predetermined level. Further,and more importantly, the positive feedback provided by the resistor 76assures prompt removal of the approximately twenty volts at the junction72, as soon as the amount of light impinging upon the light-sensitiveelement 50 rises above the predetermined level, and thus assures promptde-energization of the coil 120 of the rotary solenoid.

The position of the movable contact of the potentiometer 48 willdetermine the amount of light which must impinge upon the lightsensitiveelement 50 to cause the transistor 52 to become non-conductive; and thatmovable contact will usually be set to enable that light-sensitiveelement to cause that transistor to become non-conductive at lightlevels appreciably below potentially hurtful light levels. The positionof the movable contact of the potentiometer as will determine the firingangle which the subcircuit 109 provides for the unijunction transistor112 after the charge in the capacitor 94 has stabilized. While thatmovable contact has been set to cause the unijunction transistor 112 andthe controlled rectifier 128 to apply voltage pulses of about fifteenvolts to the coil 120, after the charge in the capacitor 94 hasstabilized, that movable contact can be set to cause that unijunctiontransistor and that controlled rectifier to apply higher or lowervoltage pulses to that coil or to another electromagnetic element whichis used in lieu of that coil.

It thus should be apparent that the light-sensitive optical, controlsystem provided by the present invention is largely insensitive tochanges in line voltage. Also, it should be apparent that the saidcontrol system senses and responds to the amount of light which impingesupon the light-sensitive element 50 thereof during each halfcycle of thealternating current applied to the plug Iii, applies relatively highvoltage pulses to the coil of the rotary solenoid during turn on andduring a limited number of half-cycles after the light-interceptingelement 132 has been in light-intercepting position, and promptlypermits that light-intercepting element to move to light-interceptingposition whenever the light impinging upon that light-sensitive elementreaches a predetermined level.

Whereas the drawing and accompanying description have shown anddescribed a preferred embodiment of the present invention, it should beapparent to those skilled in the art that various changes may be made inthe form of the invention without affecting the scope thereof.

What I claim is:

1. A light-sensitive, optical, control system which comprises:

a light-sensitive element,

a light-intercepting element that is movable into and out oflight-intercepting position,

an electromagnetic element to move said light-inter cepting elementrelative to said light-intercepting position, a subcircuit which acts asa ramp-generator, and a driving circuit for said electromagneticelement, said subcircuit responding to a given signal from saidlight-sensitive eleme't to cause said driving circuit to develop arelativ ly large voltage pulse for said electromagnetic element, toassure prompt and effective energization of said electromagneticelement,

whereby said driving circuit and said subcircuit assure prompt andeffective energization of said electromagnetic element.

2. A light-sensitive, optical, control system as claimed in claim. 1wherein said subcircuit has means therein causing said subcircuit tocause said driving circuit to progressively reduce the values of thevoltage pulses for said electromagnetic element until said voltagepulses are substantially lower than said relatively high voltage pulse.

3. A light-sensitive, optical, control system as claimed ing claim 1wherein said subcircuit has means therein causing said subcircuit to actas a current source after said subcircuit has caused said drivingcircuit to apply said relatively high voltage pulse to saidelectromagnetic element.

4. A light-sensitive, optical, control system as claimed in claim 1wherein said subcircuit has means therein causing said subcircuit tocause said driving circuit to develop a lower voltage pulse for saidelectromagnetic element to keep said electromagnetic element energized,said lower voltage pulse minimizing the heating, and the powerconsumption, of said electromagnetic element.

5. A lightsensitive, optical, control system as claimed in claim 1wherein said subcircuit includes a chargestoring element that initiallyhas a low impedance but l3 that increases the impedance thereof as itstores charges.

a A light-sensitive, optical, control system as claimed in claim 1wherein said subcircuit includes a transistor and a capacitor in theemitter-collector circuit of said transistor, said capacitor initiallybeing discharged and thus initially permitting a high level of currentflow through said emitter-collector circuit of said transistor to causesaid driving circuit to develop said relatively high voltage pulse, saidcapacitor subsequently becoming charged and thus permitting only lowerlevels of current to flow through said emitter-collector circuit of saidtransistor to cause said driving circuit to develop a lower voltagepulse for said electromagnetic element.

7. A light-sensitive, optical, control system as claimed in claimllwherein said driving circuit includes a normally noncoriductiveelement that can be fired to render it conductive, and wherein pulsatingcurrent is supplied to said driving circuit, whereby said drivingcircuit recurrently supplies voltage pulses to said electromagneticelement.

8. A light-sensitive, optical, control system as claimed in claimlwherein said driving circuit includes a normally non-conductive elementthat can be fired to render it conductive, and wherein said subcircuitincludes means thatautomatically reduces the firing angle of saidnormally non-conductive element after said driving circuit has appliedsaid relatively high voltage pulse to said electromagnetic element.

9. A light-sensitive, optical, control system as claimed in claim 1wherein said driving circuit includes a normally non-conductive elementthat can be fired to render it conductive, and wherein said subcircuitincludes a capacitor that exponentially reduces the firing angle of saidnormally non-conductive element after said driving circuit has appliedsaid relatively high voltage pulse to said electromagnetic element.

it A light-sensitive, optical, control system as claimed in claim 1wherein a light level detector includes said light-sensitive element andresponds to a predetermined change in the light impinging upon saidlight-sensitive element to apply a distinctively difierent signal tosaid subcircuit.

H. A light-sensitive, optical, control system as claimed in claim 1wherein a light level detector includes said light-sensitive element andresponds to a predetermined change in the light impinging upon saidlight-sensitive element to apply a distinctively different signal tosaid subcircuit, j'fsaid light level detector including a plurality ofstages aiid means to provide positive feedback from a subsequeiritstageto an earlier stage to effect prompt development of said distinctivelydifferent signal.

12. A light-sensitive, optical, control system as claimed in ,claim 1wherein a light level detector includes said light-sensitive element andresponds to a predetermined change in the light impinging upon saidlight-sensitive element to. apply a distinctively different signal tosaid subcircuit and wherein a voltage regulator applies a regulatedvoltage to said light level detector, said voltage regulator making theoperation of said light level detector essentially independent ofvariations in line voltage.

13. A light-sensitive, optical, control system as claimed in claim 1wherein a light level detector includes said light-sensitive element andresponds to a predetermined change in the light impinging upon saidlight-sensitive element to apply a distinctively different signal tosaid subcircuit, wherein a voltage-regulating means applies a regulatedvoltage to said light level detector, and where in a furthervoltage-regulating means applies a regulated voltage to a firing meansfor said driving circuit, the first said and said secondvoltage-regulating means making the operation of said light leveldetector and of said firing means essentially independent of variationsin line voltage.

lid. A light-sensitive, optical, control system as claimed in claim 1wherein a light level detector includes said light-sensitive element andresponds to a predetermined. change in the light impinging upon saidlight-sensitive element to apply a distinctively different signal tosaid. subcircuit, and wherein a voltage regulator applies regulatedvoltage to said light level detector, said voltage regulator making theoperation of said light level detector essentially independent ofvariations in line voltage, said voltage regulator supplying pulsatingDC. voltage to said light level detector and thereby permitting thevoltage applied to said light level detector to recurrently fallessentially to zero.

15. A light-sensitive, optical, control system as claimed in claim 1wherein a light level detector includes said. light-sensitive elementand responds to a predetermined change in the light-impinging upon saidlight-sensitive element to apply a distinctively different signal tosaid. subcircuit, wherein a voltage-regulating means applies a regulatedvoltage to said light level detector, and wherein. a furthervoltage-regulating means applies a regulated. voltage to a firing meansfor said driving circuit, the first said and said secondvoltage-regulating means main ing the operation of said light leveldetector and of said firing means essentially independent of variationsin line voltage, said first said and said second voltage-- regulatingmeans supplying pulsating voltage to said light level detector and tosaid firing means and thereby permitting the voltage applied to saidlight level detector and to said firing means to recurrently fallessentially, to zero. I

16. A light-sensitive, optical, control system as claimed in claim llwherein said electromagnetic element is the coil of a solenoid, andwherein a capacitor is connected in parallel with said coil.

17. A light-sensitive, optical, control system which come prises:

a light-sensitive element,

a light-intercepting element that is movable into and out oflight-intercepting position,

an electromagnetic element to move said light-intercepting elementrelative to said light-intercepting position,

a light level detector which includes said light-sensitive element andwhich develops signals that vary when. the light impinging upon saidlight-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount 0t light impingingupon said light-sensitive element exceeds a predetermined value, todevelop a signal which enables said driving circuit to cause saidelectromagnetic element to permit prompt and effective movement of saidlight-intercepting element into light-intercepting position, and I j avoltage-regulating means that supplies a regulated voltage to said lightlevel detector,

whereby said predetermined value of light impinging upon saidlight-sensitive element is essentially independent of changes in linevoltage.

18. A light-sensitive, optical, control system as claimed in claim 17wherein said voltage-regulating means applies said regulated voltageacross a voltage divider which includes said light-sensitive element.

19. A light-sensitive, optical, control system. which comprises:

a light-sensitive element,

a light-intercepting element that is movable into and out oflight-intercepting position,

an electromagnetic element to move said light-intercepting elementrelative to said. light-intercepting position,

a light level detector which includes said light-sensitive element andwhich develops signals that vary when the light impinging upon saidlight-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount of light impingingupon said light-sensitive element exceeds a predetermined value, todevelop a signal which enables said driving circuit to cause saidelectromagnetic element to permit prompt and effective movement of saidlight-intercepting element into light-intercepting position, and

a voltage-supplying means that supplies a pulsating voltage to saidlight level detector,

whereby the voltage supplied to said light level detector recurrentlydrops essentially to zero.

2%. A light-sensitive, optical, control system which comprises:

a light-sensitive element,

a light-intercepting element that is movable into and out and oflight-intercepting position,

an electromagnetic element to move said light-intercepting elementrelative to said light-intercepting position,

a light level detector which includes said light-sensitive element and-which develops signals that vary when the light impinging upon saidlight-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount of light impingingupon said light-sensitive element ex ceeds a predetermined value, todevelop a signal which enables said driving circuit to cause saidelectromag netic element to permit prompt and effective move ment ofsaid light-intercepting element into lightintereepting position,

a plurality of stages in said light level detector, and

means to provide positive feedback from a subsequent stage to an earlierstage to effect prompt development of said signal by said light leveldetector whenever the amount of light impinging upon saidlight-sensitive element exceeds said predetermined value.

21. A light-sensitive, optical, control system which comprises:

a light-sensitive element,

a light-intercepting element that is movable into and out oflight-intercepting position,

an electromagnetic element to move said light-intercepting elementrelative to said light-intercepting position,

a light level detector which includes said light-sensitive element andwhich develops signals thatvary when the light impinging upon saidlight-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount of light impingingupon said light-sensitive element exceeds a predetermined value, todevelop a signal which enables said driving circuit to cause saidelectromagnetic element to permit prompt and effective movement of saidlight-intercepting element into light-intercepting position, and Iavoltage-supplying' means that supplies a pulsating voltage to saiddriving circuit,

whereby the voltage supplied to said driving circuit recurrently dropsessentially to zero,

References Cited UNITED STATES PATENTS 3,191,516 6/ 1965 Corcoran350--269X 3,198,883 8/1965 Borberg et al 178-7.92X 3,377,427 4/l968Fischer 178-7.2X

OTHER REFERENCES TV Camera Protection Circuit, by Vernon I. Poehls, RCATechnical notes, RCA TN No. 459, September 1961,

JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant ExaminerUS. Cl. X.R,

